Make top half really top half and bottom half really bottom half:
Each T_readdir request handling is hopping between threads (main
I/O thread and background I/O driver threads) several times for
every individual directory entry, which sums up to huge latencies
for handling just a single T_readdir request.
Instead of doing that, collect now all required directory entries
(including all potentially required stat buffers for each entry) in
one rush on a background I/O thread from fs driver by calling the
previously added function v9fs_co_readdir_many() instead of
v9fs_co_readdir(), then assemble the entire resulting network
response message for the readdir request on main I/O thread. The
fs driver is still aborting the directory entry retrieval loop
(on the background I/O thread inside of v9fs_co_readdir_many())
as soon as it would exceed the client's requested maximum R_readdir
response size. So this will not introduce a performance penalty on
another end.
Signed-off-by: Christian Schoenebeck <qemu_...@crudebyte.com>
---
hw/9pfs/9p.c | 122 +++++++++++++++++++++++----------------------------
1 file changed, 55 insertions(+), 67 deletions(-)
diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 43584aca41..8283a3cfbb 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -971,30 +971,6 @@ static int coroutine_fn fid_to_qid(V9fsPDU *pdu,
V9fsFidState *fidp,
return 0;
}
-static int coroutine_fn dirent_to_qid(V9fsPDU *pdu, V9fsFidState *fidp,
- struct dirent *dent, V9fsQID *qidp)
-{
- struct stat stbuf;
- V9fsPath path;
- int err;
-
- v9fs_path_init(&path);
-
- err = v9fs_co_name_to_path(pdu, &fidp->path, dent->d_name, &path);
- if (err < 0) {
- goto out;
- }
- err = v9fs_co_lstat(pdu, &path, &stbuf);
- if (err < 0) {
- goto out;
- }
- err = stat_to_qid(pdu, &stbuf, qidp);
-
-out:
- v9fs_path_free(&path);
- return err;
-}
-
V9fsPDU *pdu_alloc(V9fsState *s)
{
V9fsPDU *pdu = NULL;
@@ -2337,6 +2313,18 @@ size_t v9fs_readdir_response_size(V9fsString *name)
return 24 + v9fs_string_size(name);
}
+static void v9fs_free_dirents(struct V9fsDirEnt *e)
+{
+ struct V9fsDirEnt *next = NULL;
+
+ for (; e; e = next) {
+ next = e->next;
+ g_free(e->dent);
+ g_free(e->st);
+ g_free(e);
+ }
+}
+
static int coroutine_fn v9fs_do_readdir(V9fsPDU *pdu, V9fsFidState *fidp,
int32_t max_count)
{
@@ -2345,54 +2333,53 @@ static int coroutine_fn v9fs_do_readdir(V9fsPDU *pdu,
V9fsFidState *fidp,
V9fsString name;
int len, err = 0;
int32_t count = 0;
- off_t saved_dir_pos;
struct dirent *dent;
+ struct stat *st;
+ struct V9fsDirEnt *entries = NULL;
- /* save the directory position */
- saved_dir_pos = v9fs_co_telldir(pdu, fidp);
- if (saved_dir_pos < 0) {
- return saved_dir_pos;
- }
-
- while (1) {
- v9fs_readdir_lock(&fidp->fs.dir);
+ /*
+ * inode remapping requires the device id, which in turn might be
+ * different for different directory entries, so if inode remapping is
+ * enabled we have to make a full stat for each directory entry
+ */
+ const bool dostat = pdu->s->ctx.export_flags & V9FS_REMAP_INODES;
- err = v9fs_co_readdir(pdu, fidp, &dent);
- if (err || !dent) {
- break;
- }
- v9fs_string_init(&name);
- v9fs_string_sprintf(&name, "%s", dent->d_name);
- if ((count + v9fs_readdir_response_size(&name)) > max_count) {
- v9fs_readdir_unlock(&fidp->fs.dir);
+ /*
+ * Fetch all required directory entries altogether on a background IO
+ * thread from fs driver. We don't want to do that for each entry
+ * individually, because hopping between threads (this main IO thread
+ * and background IO driver thread) would sum up to huge latencies.
+ */
+ count = v9fs_co_readdir_many(pdu, fidp, &entries, max_count, dostat);
+ if (count < 0) {
+ err = count;
+ count = 0;
+ goto out;
+ }
+ count = 0;
- /* Ran out of buffer. Set dir back to old position and return */
- v9fs_co_seekdir(pdu, fidp, saved_dir_pos);
- v9fs_string_free(&name);
- return count;
- }
+ for (struct V9fsDirEnt *e = entries; e; e = e->next) {
+ dent = e->dent;
if (pdu->s->ctx.export_flags & V9FS_REMAP_INODES) {
- /*
- * dirent_to_qid() implies expensive stat call for each entry,
- * we must do that here though since inode remapping requires
- * the device id, which in turn might be different for
- * different entries; we cannot make any assumption to avoid
- * that here.
- */
- err = dirent_to_qid(pdu, fidp, dent, &qid);
+ st = e->st;
+ /* e->st should never be NULL, but just to be sure */
+ if (!st) {
+ err = -1;
+ break;
+ }
+
+ /* remap inode */
+ err = stat_to_qid(pdu, st, &qid);
if (err < 0) {
- v9fs_readdir_unlock(&fidp->fs.dir);
- v9fs_co_seekdir(pdu, fidp, saved_dir_pos);
- v9fs_string_free(&name);
- return err;
+ break;
}
} else {
/*
* Fill up just the path field of qid because the client uses
* only that. To fill the entire qid structure we will have
* to stat each dirent found, which is expensive. For the
- * latter reason we don't call dirent_to_qid() here. Only drawback
+ * latter reason we don't call stat_to_qid() here. Only drawback
* is that no multi-device export detection of stat_to_qid()
* would be done and provided as error to the user here. But
* user would get that error anyway when accessing those
@@ -2405,25 +2392,26 @@ static int coroutine_fn v9fs_do_readdir(V9fsPDU *pdu,
V9fsFidState *fidp,
qid.version = 0;
}
+ v9fs_string_init(&name);
+ v9fs_string_sprintf(&name, "%s", dent->d_name);
+
/* 11 = 7 + 4 (7 = start offset, 4 = space for storing count) */
len = pdu_marshal(pdu, 11 + count, "Qqbs",
&qid, dent->d_off,
dent->d_type, &name);
- v9fs_readdir_unlock(&fidp->fs.dir);
+ v9fs_string_free(&name);
if (len < 0) {
- v9fs_co_seekdir(pdu, fidp, saved_dir_pos);
- v9fs_string_free(&name);
- return len;
+ err = len;
+ break;
}
+
count += len;
- v9fs_string_free(&name);
- saved_dir_pos = dent->d_off;
}
- v9fs_readdir_unlock(&fidp->fs.dir);
-
+out:
+ v9fs_free_dirents(entries);
if (err < 0) {
return err;
}
--
2.20.1
